Embodiments of the present invention relates to a rotatable-drum laundry drier, and to a method of controlling a rotatable-drum laundry drier to dry delicate laundry.
Drying delicate laundry, such as woolens or similar, in a rotatable-drum laundry drier is a risky operation, on account of the known tendency of delicate laundry to felt and/or undergo other damage. Both these tendencies depend substantially on a combination of two critical drying factors, such as drying air temperature and surface rubbing of the laundry against other laundry items or the inner wall of the drum as it rotates.
To reduce rubbing of the laundry, a method of controlling a rotatable-drum laundry drier has been devised whereby, substantially, the drum is controlled to reach, during the drying cycle, such a rotation speed that delicate laundry is pressed by centrifugal force against the inner wall of the drum, to which it adheres, so as to be prevented from sliding/tumbling inside the drum. A method of this sort is described, for example, in EP 2014822.
The above method is particularly advantageous, in that, besides reducing rubbing of the laundry inside the drum, the method also allows accurate laundry moisture measurement using electronic control systems comprising measuring sensors/electrodes fitted to the inner wall of the drum and directly contacting the laundry. That is, keeping the laundry clamped against the inner wall of the rotating drum ensures effective contact between the sensors/electrodes and the laundry and, hence, accurate moisture measurement, enabling the electronic control system to determine completion of the drying operation and, hence, when to stop the drying cycle.
Though effective, the above method is not altogether suitable for use in rotatable-drum laundry driers in which the measuring sensors/electrodes, instead of being located inside the drum, directly contacting the laundry, are connected to a stationary part of the casing in such a way to face the loading/unlading opening in the drum.
Research by the Applicant, in fact, shows that, when the above control method is implemented in a rotatable-drum laundry drier in which the measuring sensors/electrodes are located outside the drum, i.e. in a lateral position facing the opening in the drum, clamping the laundry to the rotating drum greatly reduces the probability that the laundry contacts the sensors/electrodes in such a way to effectively detect the moisture of the laundry, which may result in an incorrect laundry moisture measurement and, in some cases, as, for example, with small laundry loads, in no moisture measurement at all.
Without an accurate moisture measurement, the electronic control system is therefore unable to accurately determine when to stop the cycle, thus resulting in either incomplete drying of the laundry, or temporary overheating and, hence, felting of delicate items.
In-depth research has been carried out by the Applicant to achieve the following specific goals:                reduce felting and damage to delicate laundry, particularly woolens;        accurately measure laundry moisture, even when the moisture measuring sensors/electrodes are located outside the drum;        accurately calculate when to stop the drying cycle, even when the measuring sensors/electrodes are located outside the drum.        